🎄🎄12 Days of Xmas Quiz🎄🎄. Day 10 Question 10

[Rich B]

A clever engineer called Thomas 🤓, found that he could build something amazing using just a staircase, 29 locks and 4 lochs, all he had to do was add water…🌊
He could have been a Cutter.

What did he build ?  🤷‍♂️